U.S. patent number 4,978,921 [Application Number 07/345,738] was granted by the patent office on 1990-12-18 for electrode probe for use in aqueous environments of high temperature and high radiation.
This patent grant is currently assigned to General Electric Company. Invention is credited to Maurice E. Indig, Laura L. H. King.
United States Patent |
4,978,921 |
Indig , et al. |
December 18, 1990 |
Electrode probe for use in aqueous environments of high temperature
and high radiation
Abstract
Disclosed is an electrode probe for employment in monitoring
electrochemical potentials and which has a robust structure
particularly suiting it for employment within the rigorous
environment of the reactor core of a nuclear power facility. The
electrode of the present invention is comprised of four major
segments: a metal cap electrode, an alumina retainer, an annular
metal sleeve, and a positioning and signal transfer assembly. The
metal cap electrode has a tip portion and an annulus extending
therefrom which defines a cavity having an interior surface. The
alumina retainer has a base region with a sleeve attachment
surface, an oppositely disposed cap securing portion nestably
disposed within said cap electrode cavity and sealingly attached
thereto. The retainer further has an axis channel penetrating
therethrough from the base region to the cap securing portion. The
annular metal sleeve is formed of metal exhibiting a coefficient of
thermal expansion compatible with the alumina retainer and has an
alumina retainer surface in sealing engagement with said retainer
sleeve attachment surface and oppositely disposed outlet. An
electrical conductor is in electrical connection with the cap
electrode and extends through the retainer access channel and
through the annular metal sleeve to the sleeve outlet. Finally,
positioning and signal transfer assembly is associated with the
sleeve outlet for providing support for the sleeve and for
conveying electrical signals from the conductor.
Inventors: |
Indig; Maurice E. (Fremont,
CA), King; Laura L. H. (Raleigh, NC) |
Assignee: |
General Electric Company (San
Jose, CA)
|
Family
ID: |
23356286 |
Appl.
No.: |
07/345,738 |
Filed: |
May 1, 1989 |
Current U.S.
Class: |
324/446;
324/72.5; 204/400; 324/724 |
Current CPC
Class: |
G21C
17/10 (20130101); G01N 17/02 (20130101); Y02E
30/30 (20130101) |
Current International
Class: |
G21C
17/10 (20060101); G01N 17/00 (20060101); G01N
17/02 (20060101); G01N 027/02 () |
Field of
Search: |
;324/446,438,439,72.5,700,713,724,158P,149 ;204/1T,406,400 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Eisenzopf; Reinhard J.
Assistant Examiner: Mueller; Robert W.
Attorney, Agent or Firm: Schroeder; Robert R.
Claims
We claim:
1. An electrode probe for employment in monitoring electrochemical
potentials, comprising:
(a) a metal cap electrode having a tip portion, and an annulus
extending therefrom which defines a cavity having an interior
surface;
(b) an alumina retainer having a base with a sleeve attachment
region and oppositely disposed cap securing portion nestably
disposed within said cap electrode cavity and sealingly attached
thereto, and an access channel penetrating therethrough from said
base to said cap securing portion;
(c) a first annular metal sleeve formed of a metal exhibiting a
coefficient of expansion compatible with said alumina retainer, and
having an alumina retainer region in sealing engagement with said
retainer sleeve attachment region, said sleeve having an oppositely
disposed outlet;
(d) a first insulated electrical conductor in electrical connection
with said cap electrode and extending through said retainer access
channel and through said annular metal sleeve to said sleeve
outlet; and
(e) a positioning and signal transfer assembly associated with said
sleeve outlet for providing support for said sleeve and for
conveying electrical signals from said conductor.
2. The electrode probe of claim 2 wherein said first electrical
conductor is insulated by an annular electrical insulator housed
within said first annular metal sleeve.
3. The electrode probe of claim 2 wherein said annular electrical
insulator is formed of alumina.
4. The electrode probe of claim 1 wherein said positioning and
signal transfer assembly includes an annular stainless steel collar
welded to the outlet of said first annular metal sleeve and through
which an insulated second electrical conductor passes, said second
electrical conductor being electrically connected to said first
electrical conductor.
5. The electrode probe of claim 1 wherein a second annular metal
transition sleeve is interposed between said first annular metal
sleeve and said positioning and signal transfer assembly, said
second metal transition sleeve being formed of a different material
than said first annular metal sleeve.
6. The electrode probe of claim 5 wherein said second metal
transition sleeve is formed of stainless steel.
7. The electrode probe of claim 1 wherein said first electrical
conductor is a wire formed of a material selected from the group
consisting of platinum, a kovar, and copper.
8. The electrode probe of claim 1 wherein said metal cap electrode
is formed of a material selected from the group consisting of
stainless steel and platinum.
9. The electrode probe of claim 1 wherein said first annular metal
sleeve is formed of kovar.
10. The electrode probe of claim 1 wherein said alumina retainer is
formed from single crystal sapphire.
11. An electrode probe for employment in monitoring electrochemical
potentials, comprising:
(a) a cylindrical metal cap electrode having a tip portion, and an
annulus extending therefrom which defines a cavity having an
interior surface;
(b) a cylindrically-shaped alumina retainer having a base with a
sleeve attachment region and oppositely disposed cap securing
portion nestably disposed within said cap electrode cavity and
sealingly brazed thereto, and an access channel penetrating
therethrough from said base to said cap securing portion;
(c) a kovar annular cylindrical sleeve having an alumina retainer
region in sealing brazed engagement with said retainer sleeve
attachment region, said sleeve having an oppositely disposed
outlet;
(d) an annular ceramic electrical insulating cylinder housed within
said kovar annular cylinder substantially its entire extent;
(e) a first electrical conductor wire in electrical connection with
said cap electrode and extending through said retainer access
channel and through said ceramic cylinder to said sleeve outlet;
and
(f) a metal collar welded to the outlet of said sleeve and through
which a second insulated conductor wire passes from without to
within said annular ceramic cylinder to electrical connection with
said first electrical conductor wire.
12. The electrode probe of claim 11 wherein a stainless steel
annular transition sleeve is welded to said kovar annular cylinder,
said transition sleeve having an outlet to which said metal collar
is welded.
13. The electrode probe of claim 12 wherein said alumina retainer
is formed of a single crystal sapphire.
14. The electrode probe of claim 13 wherein said first conductor
wire is formed of a material selected from the group consisting of
platinum, kovar, and copper.
15. The electrode probe of claim 14 wherein said metal cap
electrode is formed from a material selected from the group
consisting of stainless steel and platinum.
16. The electrode probe of claim 11 wherein all surfaces to be
joined are metalized prior thereto.
17. The electrode probe of claim 11 wherein said first conductor
wire has a spring section formed at a location within said annular
ceramic cylinder.
Description
BACKGROUND OF THE INVENTION
The nuclear power industry long has been engaged in a multitude of
studies and investigations seeking improvement in the stamina and
reliability of the materials and components forming a reactor based
power system. One such investigation has been concerned with
intergranular stress corrosion cracking (IGSCC) which heretofore
principally has been manifested in the water recirculation piping
systems external to the radiation intense reactor core regions of
nuclear facilities. Typically, the piping architecture of these
external systems is formed of a stainless steel material.
Generally, these studies have determined that three factors must
occur in coincidence to create IGSCC promotional conditions. These
factors are: (a) a sensitization of the metal (stainless steel) for
example, such as caused by a chromium depletion at grain boundaries
which may be caused by heat treatment in the course of normal
processing of the material or by welding and the like procedures;
(b) the presence of tensile stress in the material; and (c) the
oxygenated normal water chemistry (NWC) environment typically
present in a boiling water reactor (BWR). This latter environment
is occasioned by any of a variety of oxidizing species contributed
by impurities in reactor coolant water. By removing any one of
these three factors, the IGSCC phenomenon is essentially obviated.
Such removal particularly has been accomplished with respect to the
latter, oxygenated environment factor, through employment of an
electrochemical potential monitoring approach combined with an
associated hydrogen water chemistry (HWC) technique providing for a
controlled addition or injection of hydrogen into the aqueous
coolant environment.
Electrochemical potential monitoring is carried out employing
paired electrochemical half-cell probes or electrodes which are
mounted within the recirculation piping or in an external vessel
which has its water source from the reactor water in the
recirculation piping the electrodes are accessed to the external
environment through gland type mountings or the like. Where, as in
the instant application, the electrode system of interest involves
the potential from a metal corrosion electrode, then the reference
electrode can conveniently be a metal-insoluble salt-electrode if
the metal salt couple is chemically stable and if appropriate
thermodynamic data is available. Accordingly, one of the
thus-mounted probes which is configured as a reference electrode
may be based, for example, on a silver/silver chloride half-cell
reaction. Once the reference electrode half cell is defined, the
cell is completed with the sensing cell portion based upon a metal
such as platinum or stainless steel. Calibration of the reference
electrode and/or the electrode pair is carried out by appropriate
Nernst based electrochemical calculations, and by thermodynamic
evaluation in combination with laboratory testing within a known
environment.
Half cell electrodes developed for use in reactor recirculation
piping traditionally have been configured with metal housings, high
temperature ceramics, and polymeric seals such as Teflon. These
structures have performed adequately in the more benign and
essentially radiation-free environments of recirculation
piping.
Over the recent past, investigators have sought to expand the
electrochemical potential (ECP) monitoring procedures to the severe
environment of the fluid in the vicinity of the reactor core itself
for the purpose of studying or quantifying the effect of
hydrogen-water chemistry adjustment in mitigating irradiation
assisted stress corrosion cracking (IASCC) as well as IGSCC. Within
the reactor core, the monitoring electrode can be mounted, for
example, with otherwise unemployed or in tandem with the traveling
instrumentation probe (TIP) of available local power range monitors
(LPRM) and the like. The monitors are located in a severe, high
temperature (typically 285.degree. C.), high pressure and high
radiation (typically 10.sup.9 R (rads) per hour gamma, 10.sup.13 R
per hour neutron) environments. Probe structures of earlier designs
are completely inadequate for this reactor core environment, both
from a material standpoint and with respect to the critical need to
prevent leakage of radioactive materials to the environment outside
of the reactor vessel.
BROAD STATEMENT OF THE INVENTION
The present invention is addressed to an electrode for evaluating
electrochemical potentials which has a robust structure
particularly suiting it for employment within the rigorous
environment of the reactor core of a nuclear power facility.
The electrode of the present invention is comprised of four major
segments: a metal cap electrode, an alumina retainer (i.e. an
insulator), an annular metal sleeve, and a positioning and signal
transfer assembly. The metal cap electrode has a tip portion and an
annulus extending therefrom which defines a cavity having an
interior surface. The alumina retainer has a base region with a
sleeve attachment surface, an oppositely disposed cap securing
portion nestably disposed within said cap electrode cavity and
sealingly attached thereto. The retainer further has an axis
channel penetrating therethrough from the base region to the cap
securing portion. The annular metal sleeve is formed of metal
exhibiting a coefficient of thermal expansion compatible with the
alumina retainer and has an alumina retainer surface in sealing
engagement with said retainer sleeve attachment surface and
oppositely disposed outlet. An electrical conductor is in
electrical connection with the cap electrode and extends through
the retainer access channel and through the annular metal sleeve to
the sleeve outlet. Finally, positioning and signal transfer
assembly is associated with the sleeve outlet for providing support
for the sleeve and for conveying electrical signals from the
conductor.
Advantages of the present invention include a probe structure
adapted to operate under the rigorous environment of the reactor
core of a nuclear power facility. Another advantage is the
ceramic/metal construction of the electrode for providing a sealing
architecture that has multiple seals to prevent leakage of
radioactive materials to the ambient environment of the reactor.
These and other advantages will be readily apparent to those
skilled in the art based upon the disclosure contained herein.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional elevation view of an electrode probe
according to the invention;
FIG. 2 is an alternative metal cap electrode for use with the probe
depicted at FIG. 1; and
FIG. 3. is a graph showing a laboratory evaluation of an electrode
according to the invention in conjunction with a standard
electrode.
DETAILED DESCRIPTION OF THE INVENTION
While having utility in a broad variety of industrial monitoring
functions, the electrode structure of the instant invention finds
particular utility operating under the rigorous environment of the
reactor core of a nuclear power facility. No elastomeric seals or
polymeric components are present in its structure which
incorporates a sealing architecture of the highest integrity. In
the latter regard, a brazed and welded assembly consisting only of
ceramic and metal parts forms the structure of the device. The
electrode finds employment either as a standard or reference
electrode, or as a sensing electrode depending upon the material
used in forming the active electrode area. For a detailed
discussion in connection with the above, reference is made to
Physical Chemistry by G. W. Castellan, Chapter 17, "Equilibria in
Electrochemical Cells", pp 344-382, Addison-Wesley Publishing Co.,
Reading, Mass. (1964).
Referring to FIG. 1, the structure of the electrode probe of the
present invention is seen to be comprised of four principal
components: metal cap electrode 10; alumina retainer 12; annular
metal sleeve 14; and positioning and signal transfer assembly 16.
Electrical signals are transferred from metal cap electrode 10
through positioning and signal transfer assembly 16 to the outside
via electrical conductor 18.
Referring to the various components in more detail, metal cap
electrode 10 can be seen to be formed of tip portion 20 and annulus
22 that extends therefrom and which defines a cavity having an
interior surface 24. Materials of construction for metal cap
electrode 10 will determine the function of the electrode device of
the present invention. For typicallyencountered boiling water
reactor (BWR) applications, use of stainless steel in constructing
metal cap electrode 10 enables the electrode probe to measure the
ECP of stainless steel in any given environment. Metal cap
electrodes fabricated from other materials could be used to form
similar sensing electrodes for measurement of ECPs of different
metals. The second general category for the electrode device of the
present invention involves the use of platinum in fabricating metal
cap electrode 10. Such an electrode device in HWC environments
enables the use of the electrode device as a reference electrode
(provided the hydrogen concentration is known) or it can be used to
calibrate other reference electrodes (e.g. an Ag/AgCl reference
electrode). Thus it will be seen that the architecture of the
electrode probe of the present invention provides design
flexibility enabling it to be adapted to function both as a sensing
electrode as well as a reference electrode, while retaining the
same overall construction advantages.
In order to provide electrical isolation of metal cap electrode 10
from other metal components forming the electrode probe, alumina
retainer 12 is used to support metal cap electrode 10. Alumina
retainer 12 desirably is formed of sapphire, which is a single
crystal form of alumina. Sapphire material not only provides
requisite electrical insulation, but also, by virtue of its single
crystal structure, is highly resistant to attack by water within
which it is immersed and, importantly, it exhibits no grain
boundaries. High purity alumina, ruby, or other materials, of
course, can be used as those skilled in the art will appreciate.
Alumina retainer 12 is seen to be formed having base region 26 and
oppositely-disposed cap securing portion 28. Cap securing portion
28 is nestably disposed within metal cap electrode 10 and in
sealing engagement with cavity interior surface 24. Advantageously,
interior surface 24 of annulus 22 is brazed to retainer cap
securing portion 28, e.g. by use of silver braze. In this regard,
it will be appreciated that all ceramic surfaces to be brazed are
metalized, e.g. with tungsten and plated with nickel, in order to
ensure adequate wetting of the surfaces to be attached by the braze
filler metal or alloy. In fact, use of multiple layers of metal
coating, especially on the mating surfaces of metal cap 28 and
alumina retainer 12, can be practiced as is necessary, desirable,
or convenient in conventional fashion. The braze seal between metal
cap electrode 10 and alumina retainer 12 should provide a hermetic
seal for ensuring integrity of the electrode probe structure and to
ensure against leakage of radiation to the outside environment. To
this end, the attachment regions of retainer 12 desirably are
painted with tungsten paint, fired, and then nickel plated.
Base region 26 of alumina retainer 12 has sleeve attachment region
30 for securing retainer 12 to annular metal sleeve 14. Again,
surface metalization and brazing with silver braze or the like is
practiced for joining attachment region 30 to sleeve 14. Retainer
12 also has access channel 25 which runs its extent from cap
securing portion 28 to base region 26. Again, it will be
appreciated that a hermetic seal needs to be formed. Sleeve
attachment region 30, then, preferably is nickel-plated, fired, and
this sequence repeated.
Annular metal sleeve 14 has alumina retainer region 32 for joining
with retainer sleeve attachment region 30. In the construction
architecture depicted at FIG. 1, sleeve retainer region 32 is
formed to have land 34 against which retainer 12 rests. It should
be observed that the dimensional tolerances for all components to
be joined is such that snug interengagement results, thus
minimizing the volume to be filled by the braze metal used in
joining the various components forming the electrode device of the
present invention.
In order to minimize thermal stress which otherwise would be caused
by virtue of the different materials of construction used in
forming retainer 12 and annular sleeve 14, annular metal sleeve 14
is formed of a metal exhibiting a coefficient of thermal expansion
compatible with the alumina retainer. Kovar comprises the preferred
metal for use in forming annular metal sleeve 14. Kovar comprises a
group of alloys, e.g. Fe 53.8%, Ni 29%, Co 17%, and Mn 0.2%, which
exhibit a coefficient of thermal expansion compatible with that of
the alumina materials used in forming retainer 12. Other materials
may be used in forming annular metal sleeve 14, providing that the
coefficient of thermal expansion between the materials is carefully
matched. It may be observed that annular sleeve 14 could be formed
of ceramic material, though cost considerations, material handling
and forming operations, and the like necessitate the use of metal
for the bulk of the structure of the electrode device. Thus, the
use of kovar in forming annular sleeve 14.
Annular sleeve 14 may be of an extent such that its outlet bears
positioning and signal transfer assembly 16. While this
construction is possible, it also is possible to reduce material
costs by joining kovar annular sleeve 14 with annular transition
sleeve 36 that can be formed of stainless steel or other high
performance alloy. Kovar sleeve 14 can be joined to stainless steel
sleeve 36 at juncture 38 by use of tungsten inert gase (TIG)
welding techniques. Again, a hermetic seal needs to result when
joining sleeve 14 to sleeve 36.
It will be observed that the components thus-far described
preferably are cylindrical in shape, though it will be appreciated
that sleeves 14 and 36, and retainer 12 can be square, hexagonal,
or of other geometric configuration. For that matter, the same
geometric variation also applies to cap electrode 20.
The lower end of stainless steel annular sleeve 36 is seen to
terminate with neck 40 which serves as the outlet for sleeve 36.
Positioning and signal transfer assembly 16 is associated with neck
40 of annular sleeve 36 and is seen to be formed from cylindrical
stainless steel collar 42, such as by TIG welding. Ceramic support
44, inwardly adjacent to collar 42, houses electrical connection
from the outside to the interior of the electrode probe of the
present invention. Specifically, insulated retainer 48 houses a
nickel tube which is connected at its lower end to the current
conducting wire of cable 46 and to its upper end to electrical
conductor 18. Assembly 16 is commercially available and marketed,
for example, by ReutorStokes, a division of General Electric
Company, Twinsburg, Ohio.
In order for electrical connection to be maintained between
electrode cap 10 and cable 46, electrical conductor 18 is provided,
preferably with spring section or coil 50 to ensure that the
electrical conductor is pushing against cap 20 and assembly 16,
thus ensuring good electrical connection. Conductor 18 suitably can
be made from copper, kovar, platinum, or other material which is
electrically conductive. While an electrical conductor can be
insulated directly, the preferred structure depicted at FIG. 1
shows annular electrical insulator 52 disposed within annular
sleeve 14 and annular sleeve 36. Electrical insulator 52 preferably
is made from a ceramic material, such as alumina, in order to
ensure electrical isolation of electrical conductor 18. While the
proximal end of electrical conductor 18 is electrically connected
to assembly 16, the distal end of electrical conductor 18 passes
through the annulus formed within sleeves 36 and 14, thence through
access channel 25 provided in retainer 12 to cap electrode 20.
Conductor 18 preferably is welded or brazed directly to the
interior side of tip portion 20 of cap electrode 10. Alternatively,
as depicted at FIG. 2, cap electrode 10 can have hole 54
penetrating through tip portion 20. Conductor 18 would be placed
within hole 54 and brazed or welded in place to provide electrical
connection therewith. The integrity of the seal, again, should be
hermetic in nature.
With respect to performance specifications of the inventive
electrode probe, the probe is designed to operate at temperatures
ranging up to about 600.degree. F. and pressures of up to about
2,000 psi. When metal cap electrode 10 is formed of platinum for
producing the reference electrode device, the novel electrode
device exhibits a voltage that is within .+-.0.020 volts of the
theoretical value for the platinum reference electrode. In use as a
reference electrode with a platinum cap, the inventive electrode
probe is capable of measuring ECPs to within .+-.0.010 volts in
constant water chemistry. In attaching cap 10 manufactured of
platinum, it should be rhodium plated and then silver brazed to
W/Ni coated cap securing portion 28.
Referring to FIG. 3, two sensing electrode probes were fabricated
in accordance with the precepts of the invention utilizing
stainless steel for metal cap electrode 10 and these probes
subjected to laboratory testing utilizing a standard Cu/Cu.sub.2 O
reference electrode. The aqueous medium for testing was provided by
an autoclave within which temperature and water chemistry were
controlled. The test was carried out at a water temperature of
274.degree. C. and in conjunction with a sequence of aqueous
conditions wherein certain dissolved gases were introduced. A first
such dissolved gas was hydrogen, as labeled along the elapsed time
portion of the figure as represented at 56, and represents hydrogen
water chemistry. Thereafter, as labeled along the elapsed time
portion of the figure as represented at 58, oxygen was injected
into the aqueous medium, thus subjecting the probes to normal
boiling water chemistry. As the potential of the reference
electrode can be calculated, its potential under the various water
conditions can be subtracted from the voltage obtained, thus
enabling a measurement of the ECP of the stainless steel electrode
probes. The results of the three probes evaluated are represented
at 60, 62, and 64. It will be observed that a shift in the ECP
results by virtue of the water chemistry involved. It is this shift
that is monitored during use of the sensing electrode probes for
determining the water chemistry of the aqueous medium being tested.
The expected shift in ECP can be seen by reference to FIG. 3.
Since certain changes may be made in the above-described apparatus
without departing from the scope of the invention, the description
and accompanying drawings shall be interpreted as illustrative and
not in a limiting sense in accordance with the precepts of the
invention disclosed herein.
* * * * *